Figure 1.

Schematic diagram of the processes underlying water transport by salivary gland acinar cells. Two identical cells are shown; cell i shows the relevant ion channels and transporters, while cell j shows the principal components of the ${\mathrm{Ca}}^{2+}$ response. Although the two sets of processes are separated here for clarity, all the processes are present in all salivary gland acinar cells. Abbreviations are PLC (phospholipase C); ${\mathrm{IP}}_3$ (inositol trisphosphate); IPR (${\mathrm{IP}}_3$ receptor); ER (endoplasmic reticulum); SERCA (sarcoplasmic/ER ${\mathrm{Ca}}^{2+}$ ATPase); KCa (${\mathrm{Ca}}^{2+}$-activated ${\mathrm{K}}^{+}$ channel); ClCa (${\mathrm{Ca}}^{2+}$-activated ${\mathrm{Cl}}^{-}$ channel); NKCC1 (${\mathrm{Na}}^{+}$/${\mathrm{K}}^{+}$/${\mathrm{Cl}}^{-}$ cotransporter); NHE1 (${\mathrm{Na}}^{+}$/H${}^{+}$ exchanger); AE4 (anion exchanger). We note that these channels and exchangers are not the only ones present in the cell but are the components that are believed to be the most important for the control of water transport in this cell type. Thus, other channels and exchangers (such as, for example, RyR or Na/Ca exchangers) that are known to be critical in other cell types are not included here.